126 FUNGOID PESTS OF CULTIVATED PLANTS. 



Plum-tree Rust. 

 Puccinia Pruni (Pers.), PI. XI. fig. 15. 



Nearly all kinds of Plum trees are subject to the ravages of the Plum- 

 tree rust, but those attacks are not in all cases equally virulent. One 

 tree may be seen in an orchard with hardly a leaf untouched, whilst 

 another tree at twenty yards' distance will scarcely reveal a pustule. 



The under side of the leaves are generally closely sprinkled with the 

 pustules, which split irregularly and discharge the spores, light brown or 

 rusty-brown for the uredospores, dark brown for the teleutospores, in 

 both cases powdery, and soon sprinkled over the leaf. 



The uredospores are egg-shaped or Pear-shaped, and the whole sur- 

 face minutely spiny (20 35 x 12-16 /x). These are the ordinary uredo- 

 spores, or, as we might call them, the true uredospores. In order to 

 meet a difficulty certain authors have recently professed that two kinds 

 of uredospores are known, the second and last invented kind being 

 elongated and of a Uromyces type, so much so that it has acquired the 

 name of Uromyces Amygdali. Whether this is also a Uredo form of 

 Puccinia Pruni docs not interest us much, as we intend, in this place, to 

 treat them as distinct diseases. 



The teleutospores are divided in the centre into two cells, each of 

 which is nearly globose, except at their junction, where they are flattened, 

 the lower cell being a little the smaller. The cell coat is chestnut-brown 

 and thickly covered with rather rigid obtuse spines (30-45 x 17 25 /<). 

 At first the short uncoloured pedicels are distinct, but these finally dis- 

 appear. 



Known in Europe, North America, India, Cape Colony, Australia, and 

 Tasmania. 



McAlpine I'm,,,. Bis. 23 ; Journ. B.H.S. xxvi. (1902), p. 963 ; Sacc. 

 Syll. vii.; Plowr. Brit. Ured. 193 ; Mass. PL Bis. 251, fig. 64 ; Cooke 

 Ihlhk. No. 1511 ; Cooke M.F. 211 ; Tubeuf, Dis. 355. 



Plum Pockets. 

 Exoascvs Pruni (Fckh), PL XL fig. 13. 



Berkeley recognised this disease in LS70. The pockets, or "bladder 

 Plums," appear soon after the fall of the flowers, attaining full sizeabout 

 the end <iC .lime, ami then soon falling from the tree. They are at first 

 nearly globose, soon becoming elongated, and often somewhat curved, 

 from one to two inclii is iii length, and a half to one inch in diameter. 

 They much resemble the proper fruit when young, except in being 

 yellowish or reddish in colour. With age the colour changes to grey, and 

 the surface looks mealy or frosted, and wrinkled. Ultimately they turn 

 nearly black, and in two or three days fall to the ground. The walls of 

 the bladders are thick, permeated by mycelium, which also enters the 

 hollow centre, and there is no stone. The fruits are evidently taken 

 possession of by the fungus at an early stage, seed production arrested, 

 and hollow bladders produoed, which have some resemblance only to 

 fruit. 



The mycelium is of the usual kind, and may be found in the smaller 



